1. Field of the Invention
The invention is concerned with improvements in valve assemblies of the type wherein a movable valve element, for example a reciprocal spool, of a fluid flow regulating valve is displaced by a fluid medium. More particularly, the present invention is concerned with such a valve wherein movement of the reciprocal spool is controlled by displacement of fluid simultaneously on each end of the spool and without pressure being applied thereto. The fluid flow to and from each end of the valve spool is controlled by servo valve means operating off the servo valve pilot pressure fluid source. The present invention is particularly concerned with such a system wherein fluid displacement alone causes movement of the reciprocal spool of the main valve rather than pressure applied to the main valve.
2. Prior Art
It is known to control the pressure of fluid which displaces the spool of a fluid flow regulating valve by means of one or more pilot valves which can be hand actuated or remote-control actuated to select the pressure of fluid acting on the spool and hence to control the position of the spool relative to the body of the fluid flow regulating valve. In such systems, the regulating valve often employs a spring or added biasing means for urging the spool towards a neutral position.
It is an advantage of such valve assemblies that the pilot valve can be mounted at any desired distance from the fluid flow regulating valve. Also, the pilot valve can be adjusted to any one of a number of different positions to ensure that the pressure of fluid acting upon the spool of the fluid flow regulating valve can be accurately selected.
With many of the prior art valve assemblies the movement of the main spool in the regulating valve from the neutral position to other positions necessitates the application of substantial fluid pressure. Generally, a substantial fluid pressure must be applied to displace the spool to the extent which is necessary to cause the spool to reach an intermediate position. When the spool is to be caused to move beyond an intermediate position, it begins to establish or terminate the flow of fluid between one or more fluid admitting and/or discharging ports. The fluid pressure which is necessary to affect such displacement of the spool is a function of the deformation or stressing of the biasing means in the pilot valve. This deformation detracts from the overall deformation of the biasing means.
It would be advantageous if a servo valve actuated main valve was designed which was independent of fluid pressure. The present invention is particularly concerned with an improvement in a valve assembly which does not operate through application of pressure to the main spool valve and thus is completely free of the above-mentioned disadvantages.